Metabolism Of Kidney Flashcards by Emily Mosher

Blood supply differences in kidney

. 90-95% of renal blood passes through cortex and uses 8% of oxygen in blood
. 5-10% of renal blood passes through medulla and uses 80% of oxygen in that blood
. Medulla more vulnerable to anoxic shock

How well did you know this?

Not at all

Perfectly

Roles of kidney

. Makes urine to excrete waste, regulate serum pH, electrolytes, and water
. Has enzymes for gluconeogenesis
. Acts as endocrine gland: synthesizes and releases EPO, renin
. Contains enzymes for vit. D metabolism important for serum Ca, ,phosphate, and bone metabolism regulation

How well did you know this?

Not at all

Perfectly

Components of urine synthesis

. Filtration
. Reabsorption
. Secretion

How well did you know this?

Not at all

Perfectly

Sequence of events in filtration

. Blood enters afferent arterioles
. GFR depends on bp
. Filters through 3 layers
. Capillary endothelium: 100x more permeable than other capillaries
. Basement membrane: composed of highly negatively charged glycoproteins and proteoglycans
. Single layer of epithelial cells (podocytes) w/ foot processes that interdigitate w/ one another

How well did you know this?

Not at all

Perfectly

What gets filtered in kidney?

. 20% plasma volume through kidney forced through filter to become ultrafiltrate
. Collects in Bowman’s capsule

How well did you know this?

Not at all

Perfectly

Ultrafiltrate contents

. Plasma H2O

. Small solutes (glucose, NaCl, urea, AA)

How well did you know this?

Not at all

Perfectly

Ultrafiltrate does NOT contain _____

. Cells or cell-like structure

. Proteins beyond a certain limit ( larger and neg. charges proteins do NOT go through)

How well did you know this?

Not at all

Perfectly

Glomerular filtration rate

. Measured by injecting radioactive substance that’s filtered in kidney and not reabsorbed by tubules
. Takes blood samples over several hours
. dec. GFR is sign of diminished kidney function

How well did you know this?

Not at all

Perfectly

Reabsorption in kidney

. Movement of material from tubule lumen into capillary
. Much if what is filtered is reabsorbed
. Requires energy

How well did you know this?

Not at all

Perfectly

Secretion in kidney

. Movement of material from capillaries into tubule lumen

. Requires energy

How well did you know this?

Not at all

Perfectly

Modes of transport in kidney tubules

. Primary active transport (NA-K-ATPase)
. Secondary active transport (glucose/Na cotransport and amino acid-Na cotransport)
. Pinocytosis and endocytosis

How well did you know this?

Not at all

Perfectly

Important indicators of renal function

Levels of urea and creatinine

How well did you know this?

Not at all

Perfectly

Azotemia

. Asymptomatic

. Nitrogenous waste products that accumulate in patient’s serum

How well did you know this?

Not at all

Perfectly

Uremia

. Symptomatic (nausea and vomiting) nitrogenous waste product build up in patient’s serum

How well did you know this?

Not at all

Perfectly

Renal threshold

. Substance that are absorbed have limit to rate at which solute can be transported
. When limit is surpassed the excess is secreted
. Glucose threshold is 220 mg/dl

How well did you know this?

Not at all

Perfectly

Endogenous compounds secreted by tubules in kidney

. Urate, creatinine, bile acid salts

How well did you know this?

Not at all

Perfectly

Exogenous compounds secreted in kidney tubules

. Penicillin

. Salicylate

How well did you know this?

Not at all

Perfectly

What determines final composition of urine?

. Excretion = filtration-absorption+secretion

How well did you know this?

Not at all

Perfectly

PH of urine is between _____

4.4 and 8

How well did you know this?

Not at all

Perfectly

Reabsorption of bicarbonate

. Most passes through filter and is reabsorbed by transporters in tubule cells

How well did you know this?

Not at all

Perfectly

Kidney excretion of phosphate and other acids

. Molecules that have pK in range of pH of urine can pick up proton and carry out in urine
. Occurs w/ any acid that can bind H and carry it out in urine

How well did you know this?

Not at all

Perfectly

What happens in kidneys during diabetic ketoacidosis

. Inc. of ketones
. Compounds filtered and appear in tubule fluid
. As urine pH dec., these compounds begin to serve as buffers that can carry H out of body in urine

Excretion of ammonia/ammonium

. NH4 is major urinary acid (1/2-2/3 daily acid load excreted w/ this)
. Preserves Na and K reserves in prolonged acidosis (other acids need this)

Aerobic vs. anaerobic metabolism in kidney

. Uses 10% of O2 the body uses
. Renal cortex more highly oxidative then medulla
. Medulla depends on glycolysis and is sensitive to low [O2]

Glucose utilized in renal medulla is produced in ___

Renal cortex

Major renal fuel used in normal (fed) person

Lactate (45%)

Major renal fuel in acidosis

Glutamine

Major renal fuel in a fasted state

. Fatty acids

Gluconeogenesis in kidney

. Can make 20-50% as much glucose as liver . Predominantly associated w/ cortex . Cortex is highly oxidative tissue w/ high ATP synthetic ability . Substrates: Gln, lactate, citrate, alpha-ketoglutarate . Important in starvation and acidosis

If acidosis is treated w/ alkali administration, then renal gluconeogenesis is___

Not stimulated

Non-excretory mechanism for kidney pH regulation

. Conversion of certain organic acids to glucose

Glutamine in kidney

. Gln taken up from blood | . Renal uptake regulated by pH (inc. uptake w/ acidosis) and glucocorticoids (stimulate glutaminase and Gln metabolism)

Glutamine metabolism in kidney

. Glutaminase converts Gln to Glu and releases 2 NH3 molecules for H excretion . Glutamate dehydrogenase converts Glu to alpha-ketoglutarate that can be used in ATP or as substrate for gluconeogenesis

Erythropoietin

. Polypeptide hormone . Synthesized in response to reduction in renal PO2 . Stimulates bone marrow to inc. production of erythrocytes

People w. Impaired renal function and anemia are given ___

Exogenous EPO

Renin

. Protease . Made in response to signals from granular cells that ac as intrarenal baroreceptors . When pressure drops the synthesis of renin is stimulated

Renin-angiotensin system

. Angiotensinogen (plasma protein in liver) gets cleaved to angiotensin I through renin . angiotensin I is converted to angiotensin II via angiotensin-converting enzyme (ACE)

Rate limiting step in RAAS

Renin

Where does RAAS occur?

. Exists in plasma and vascular surface of blood vessels throughout body, esp. in kidneys

Angiotensin II functions

. Potent vasoconstrictor, inc. bp . Inc. synthesis of aldosterone, steroid hormone, that inc. Na reabsorption . Inhibits renin synthesis

ACE inhibitors

. Captopril . Benazepril . Enalapril

Angiotensin II receptor blockers

. Irbesartan . Candesartan . Losartan . Valsartan

Vitamin D

. Dietary or synthesized from cholesterol in skin . Regulates serum Ca and phosphate . Interacts w/ bone, kidney, and intestine . Promotes absorption of Ca in intestine . Liver converts it to circulating form of Vit D Kidney converts it to active or inactive form

Vitamin D deficiency

. Causes inability to absorb dietary Ca | . Results in bone loss

Chronic renal failure in relation if vit. D

. Results in Inability to produce active vit D . Bone Ca becomes depleted . Inc. retention of Pi because kidney can’ excrete it causing high serum phosphate . When Pi is hig, less Ca can remain in solution . Leads to bone loss and soft tissue calcification . Treatment: high Ca diet, vit. D supplements, Pi reduction w/ Pi binding antacids

Symptoms associated w/ kidney failure

``` . High bp . Back pain just below rib cage . Frequent urination . Rusty or brown colored Urine . Swelling edema of the feet and ankles ```

Serum levels elevated in patients w/ kidney failure

. Urea . Creatinine . Uric acid

Urinalysis of someone w/ chronic kidney disease

. GFR dec. w/ inc. damage . Urinary protein inc. . Urinary blood cells inc. . Urine volume (too little not enough filtration, too much means inability to concentrate urine)

Oliguria

Very little urine production

Kidney not filling endocrine duties will cause ___

. Lack of EPO: low hematocrit, low rbcs, tiredness, malaise | . Lack of kidney function: hypertension

Acute renal failure

. Rapid and usually reversible deterioration of renal function . Pre-renal causes: blood loss, hemorrhage, CHF . Renal causes: bacterial infections, intoxins, rhabdmyolysis . Postrenal: cancer, obstruction of ureter

Rhabdmyolysis

. Damage to skeletal muscle causing myoglobin release . Appearance of myoglobin in blood and urine . Myoglobin extremely damaging to kidneys . Caused by: trauma, excessive exertion in heat, crush syndrome

Chronic renal failure

. Slower, progressive, irreversible loss of renal function . DM causes 40% cases, hypertension 20% . 5 stages (1 being slight damage, 5 requiring dialysis or transplant)